1. Field of Invention
The current invention relates generally to apparatus, systems and methods for generating sound. More particularly, the apparatus, systems and methods relate to placing two separate drivers a certain number of crossover frequency wavelengths apart. Specifically, the apparatus, systems and methods provide for a tweeter driver and a woofer driver side-by-side to produce a broad field of sound, left-to-right and up-and-down particularly at the crossover frequency.
2. Description of Related Art
For eons people have enjoyed good feelings that can come from good sound such as music. There are mental associations with music and sounds such emotional responses to life events such as love and losses, great pursuits, and simpler times associated with different sounds. As a result of listening to quality sounds biochemical changes in the brain can occur, resulting in the elevation in levels of endorphins and enkephalins to enhance the experience of listing to those sounds.
Because of the great enjoyment people associate with music and other sounds, extensive efforts over time have been made to improve sound production and reproduction. One key element of sound reproduction is the speaker. An important goal in reproducing sound is to produce proper balance of lower (bass), mid, and upper (treble) audio frequencies. Drivers such as woofers, midrange drivers, and tweeters are commonly used to reproduce sounds. Additionally crossover networks, both passive and active, can be used with the intent to produce the same magnitude of sound (SPL=Sound Pressure Level, such as measured at one meter with one watt drive) across the audio spectrum (e.g. 20 Hz-20 KHz), while maintaining balance of impedances and phasing as best as possible, and reducing power loads on devices such as the tweeter.
Unfortunately, due to how sounds travel on electromagnetic waveforms the listening area has nulls (as well as peaks), sometimes dramatic, at/near the crossover point(s) frequency(s). The sound at the crossover frequency is not evenly distributed to the audience on the up and down elevation patterns and/or the left & right azimuth audio signal patterns and the audience can hear these defects. Additionally, these sound field inconsistencies can also occur at frequencies other than at the crossover point. Audiences are delighted in their musical experience when the problem is mitigated or resolved.
It is unfortunate that the prior art method(s) for mitigating this otherwise highly inconsistent sound distribution was to use many drivers in a tall vertical array (long horizontal array in larger auditoriums, etc.), or using long ribbon, planer and similar drivers. These improvements are all quite large and expensive, and still have focused pattern and imaging problems at times. Digital Signal Processing (DSP) solutions require circuitry and multiple drivers and are therefore also very expensive.
FIG. 1 illustrates the well know prior art of how to determine the angle of a cancelation axis. In this example, the crossover frequency is 1700 Hz with a wavelength of about ˜=8″ (assuming with speed of sound at ground level ˜=1126 feet per second). A Tweeter T is positioned above a Woofer W and they are positioned one crossover wavelength (8 inches) apart center-to-center. A first waveform WF1 is shown emitted from the Tweeter T along a first waveform axis WFA1 and a second waveform WF2 is shown emitted from the Woofer W along a second waveform axis WFA2 that is parallel to the first waveform axis WFA1.
The right triangle formed by points P1, P2 and P3 is used to determine the cancellation axis. It is known that the cosine of angle “a” is the cosine of the line segment formed by points P2/P3 divided by the line segment formed by points P1/P2. Line segment P1/P2 is 8 inches (T & W separation). Waveform WF1 from the Tweeter T and the second waveform WF2 from the Woofer W are simultaneously both at peak values at points P2 and P1 respectively. When the first waveform WF1 and the second waveform WF2 cross line segment P1/P3 they are ½λ out-of-phase. Because the two waveforms are ½λ out-of-phase when crossing segment P1/P3, P2/P3 is 4 inches. Therefore angle “a”=cosine ((segment P2/P3)/(segment P1/P2))=cosine (4 inches/8 inches)=60° and the “angle of cancelation” is 90−60°=30° and in FIG. 1 points in the direction of line CA that is parallel to the first waveform axis WFA1 and the second waveform axis WFA2.
As illustrated in prior art FIGS. 2 and 3, even if the woofer W and tweeter T individually produce a rather broad sound field pattern, their sound fields interact at and around the crossover frequency point (where both drivers are producing sound) forming elevation pattern nulls. The only resultant broad sound fields are horizontal in pattern and only in the lobes LBs. FIG. 2 is a prior art example partial elevation view of a first person FP located in a lower location than a second person SP in an elevated location in a theater. This FIG. 2 illustrates how the lobes LBs form cancelation axes in a vertical plain. This figure illustrates a first person P1 is in a first cancellation axis CA1 so that his audio level/quality is poor and the second person P2 in a second cancellation axis CA2 so that his audio level/quality is also poor. FIG. 3 illustrates how the lobes LBs form cancelation axes in a horizontal pine if the prior art speaker is placed sideways. This figure illustrates a third person P3 is in a third cancellation axis CA3 so that his audio level/quality is poor and the fourth person P4 in a fourth cancellation axis CA4 so that his audio level/quality is also poor.
FIG. 4 illustrates a prior art system that corrects for cancelation axes by using a passive line array 400 with multiple ribbon/planar/waveguide coherent wave drivers 410. This system is rather large and very costly so it is not practical in many situations. It is similar to long ribbon and planar speakers that are also large and very expensive. However, when they are employed they can produce rather straight wave fronts 420 with reduced cancellation axes resulting in a good audio reception at a fifth person P5 that is positioned within the range of this line array 400. However, one needs to be substantially directly in the line of broadcast of this system; if one is above or below (or often, also off to one side of the wave front) the audio is reduced, quality is poor.
Another prior art system uses a line array of “spherical wave” non-coherent drivers. The result is a less acutely lobular pattern than such as FIG. 2. Undesirably, this approach is also expensive and rather large; it is often not practical to use this approach.
FIG. 5 illustrates a variant of line array 400 of FIG. 4 placed with drivers physically moved into a curved formation. Similar to the passive line array 400 of FIG. 4, it produces fairly uniform waveforms 520 with reduced cancellation axes but here with somewhat broader sound pattern forward of the inter-driver axis. However, these systems are rather large and are very expensive.
Therefore what is needed is a less costly, smaller, and better solution of reproducing consistent (sensed) sound field level/quality audio sound.